STUDY OF FREE-RANGING SHARKS 



451 



Table 1. Determination of transmitter position using measurement of 

 pulse-arrival times. 



*Pulse arrival times are known only relative to one another. 



tRequires a system such as transponding or timefix. 



+ Presence can be confirmed as within maximum transmitter range. Distance can be 



roughly estimated by signal strength, but this is subject to gross variability depending on 



propagation conditions. 

 II LOP = line of position. 

 f Often one of the two points can be ruled out, e.g., by previous fix location, by water 



depth, or by being on land. 



350 m A of current flowing (from a 6-V battery), the 0.3-mm stainless steel 

 wire deplates to the breaking point in about 60-90 s, causing the transmitter 

 to eject from a base plate and float to the surface. 



An alternative method is to use a tiny explosive squib to operate a 

 transmitter-release mechanism. One such miniature explosive piston actuator 

 (Holex, Inc., Hollister, CA) measures .53" long, .135" diameter, and fires 

 in 15 msec with an applied current of 2.0 A (squib resistance, 0.65 ohm). 

 This device can be fired by the circuit in Figure 19 if the SCR current- 

 limiting resistor is removed. 



The question of whether to plan for transmitter recovery is based on the 

 tradeoff between the advantages of recovery and the disadvantages of what is 

 needed to effect recovery. Advantages include savings in cost and time, 

 added trackings possible with reuse of units, and the opportunity to inspect 

 units that have been through actual trackings. Disadvantages include added 



